Currently sizing a PRV on a fire case scenario for a formalin storage tank having the following mass percent composition:
Methanol: 15% (stabilizer)
Tank operating conditions: 50 Celcius, 0.15 barg
Tank design pressure: -0.05/0.25 barg
I need to obtain the following properties to apply the API STD 2000 (to obtain the relief flow rate in Nm3/hr of air): average molecular weight, bubble point temperature and mass latent heat of vaporization (kJ/kg).
I got these compositions from supplier datasheets online so I believe that at these conditions, the stream should be a single phase liquid. I've tried modified UNIQUAC, Peng Robinson, Raoult's law and NRTL and in all cases I get a two phase stream.
Perhaps I'm wrong. Any help solving this matter and/or general insight into PRV sizing for formalin storage tanks would be greatly appreciated.
Thank you for your time,